Directional antenna array



April 29, 1947. H. ca. BUSIGNIES Z,419;572

DIRECTIONAL ANTENNA ARRAY Filed March 12, 1942 s Sheets-Sheet 1 INVENTOR.

f/[IVE/ 6- EUSIG'lV/ES V typeior use in direction finders.

DIRECTIONAL ANTENNA ARRAY Henri G. Busignies, Forest Hills, N. Y., assignor to Federal Telephone and Radio Corporation, a corporation of Delaware Application March 12, 1942., Serial No. 434,427

Claims.

. The present invention relates to directional antenna arrays and more particularly to arrays comprising vertical dipoles for vdirection finders and the like. Y

It is an N object of the present invention to provide an antenna array of the vertical dipole It is a further object to provide such an array which shall be comparatively free from the influence of horizontally polarized wave energy.

It isalso an object to provide such an antenna array which shall be comparatively ireefrom sq-called high antenna effect. I I

In general it is an object to provide a directional array comprising two vertical dipoles coupled to a two-conductor transmission line and associated with conductive means of suchform that said array shall deliver to said line a transverse current (i. e., one which flows in one conductor and out the other conductor in balanced fashion) preferably proportional to the difierence between the vertical polarized wave energy arriving at a given instant at each of the two dipoles and which shall be comparatively free from the production of parallel currents over the two conductors of such transmission line.

It is a further object, of the invention to provide; such an array which shall be suitable for to {horizontal polarizations and more nearly free from omni-directional reception due to high antenna effect than previously known arrays of hisp .The. socalled H type Adcock antenna, as

previously constructed, usually has two shielded transmission lines each having one transposition therein, said lines extending horizontally at right an les to one another across the center of the array, and four vertical dipoles connected to the four ends'of such shielded transmission lines.

The output for such antenna is taken from two.

downwardly extending shielded transmission lines respectively connected to thecenters of the two horizontal lines. The two outputs'are usually applied directly orthrough transformers, to sta-' tors of a so-called goniometer or crossed-statori vario-"coupler. Alternatively, theH type .Adcock maycomprise only two dipoles and only one 1 horizontal transmission line thus yielding only one output. In such case the complete array is rotatable if intended to be used for direction finding purposes.

invention comprises adding cross-link conductors to more closely interconnect the two perpendicularly disposed horizontal transmission lines 'thus' forming a sort of horizontal web, and preferably Figs. land 2 are three dimensional vectorl diagrams useful in explaining the invention; Fig. 3 represents a simple H type Adcock array of prior art type;

Figs. 4 and 5 are plan views of simple H type Adcock arrays modified in accordance with different forms of my invention;

prior art;

Figs. 7 and 8 are schematic diagrams useful in. explaining the manner in. which horizontally} polarized energy could act upon the type of array shown in Fig. 6;

' Fig.9 is a planview of a four-dipole array such as would beobtained by combining two of the simple arrays shown in Fig. 3, said array being modified in accordance with my invention to.

minimize sensitivity to horizontally polarized energy and high antenna efi'e'ct;

Fig. 10 illustrates a preferred coupling arrangement to be used in the arrays of Figs. 4, 5 and 9 I .Fig. :11 represents a prior art Adcock array I similar to that in Fig. 3 but modified to more clearly illustrate the occurrence of the high an-&

tennai efiect; r V

Fig. 12 represents an imaginary structure useful in explaining the action of my invention;

Fig. 13 represents thevoltage distribution along the shields of the structures of Fig. 11 and Fig. 12; Fig. 14 representsa conductive network which is of a somewhat different shape from that shown M in Fig. 9.

In order to clearly understand the nature of my invention it is desirable to consider in detail the nature of the errors which occur'with the N In general, the errors observed in connection with Briefly, the improvement contemplated by my best be Fig. 6 represents an improved isolated-dipole type otHAdco'ck array in accordance-Withthe H' type Adcock antennaas hitherto constructed.

such H type Adcock antenna are produced by two causes: the reception of horizontally polarized energy and the omni-directional reception of vertically polarized energy in non-difierential manner by virtue of the so-called high antenna effect. Both such forms of reception would theoretically be cancelled if there were absolutely perfect balance between the two dipoles of a pair, the two halves of each dipole, both sides of each transmission line and the shield, and the two sides of the receiving apparatus, such as transformers, goniometer, stators, etc. As a practical matter, a very small degree of unbalance is unavoidable in respect to each of these supposedly symmetrical arrangements and, as a result of such unbalance, very substantial errors in the direction observed may take place.

It is an object of the present invention to reduce the magnitude of such errors for a given accuracy of balance of the several parts of the sys tem.

For a better understanding of the manner :in which such errors are reduced, in accordance with my invention, a detailed analysis of the production and reception of horizontally polarized energy, as well as an analysis of the high antenna effect, will be useful. Fig. 1 shows the manner in which horizontally polarized energy occurs in a wavewhich was originally transmitted with vertical polarization but which has been reflected from the Heaviside layer so as to arrive in a downward direction with a partially rotated direction of polarization. The line PO represents the direction of propagation of the arriving wave, this, line being inclined at an angle g with respect to the horizontal. The line Q is the projection of PO on the l 1 orizontal or ground plane B..C. The vector ON represents the magnitude and direction of the electro-static vector E, 61? being the projection of this vector upon horizontal plane 13-0 and ON" being the projection of this vector upon the line FG which is normal to Q0 and is the line of intersection of the plane BC and the plane FL, which latter is normal to the direction PO a t the point 0.

In-similar manner the vector OM represents the electro-magnetic vector H, its projection on the horizontal plane BC being OM and its projefipn on t h e line FG being OM". The vectors ON and OM lie in the plane FL since both the electro-magnetic and electro-tstatic vectors are perpendicular to the direction of propagation, as is well known. The line OK represents the. trace which would be made in oblique plane FL by passing a vertical plane through the point 0 so as to contain the lines Q0 and P0.

The angle it represents theangular deviation of the electro-static vector ON from thegie OK. Ifthis angle a were zero so that vector ON coincided with the line OK the polarization would be spoken of as vertical p ol arization, in spite of the fact that the vector ON would still not be perpendicular to the plane BC. If the angle a is 45 the polarization of the wave is said to have IS-degree polarizatio r although again the inclination of the vector ON with respect to the horizontal (i. e., the angle NON) would be different from 45.

As is clear from an i nspection of Fig. 1 the electro-static vector O N may be resolved into 4 nent thereof. The vertical comporgt N 'N has, for convenience, been redrawn as OV extending upward from the center of the diagram. The magnitude of the horizontal component W can be readily shown to be E (305 -5111 g-l-sin a while the magnitude of the vertical component W01 6v can- .be shown to be E cos a-gg g. The angle w of the horizontal component ON with respect to the line FG is are tan (cot a'sin g).

In similar fashion, for the magnetic vector H y it can be shown that the horizontal component two vectors ON and NN, the first of these being OM is H sin a-sin g-l-cos a, that the vertical component MM is H sin a-cos g, and that the angle u of OM" with respect to the lin FG is are tan (tan a-sin 9).

Referring now more particularly to Fig. 2 which represents the manner in which the different components of the electro-static vector E aifect an Adcock antenna, it will be noted that the ground plane BC, the direction of propation P O and the vertical and horizontal components 0V and ON of the electro-static vector are illustrated exactly as in the case of Fig. 1, the reference characters employed being the same to facilitate comparison. For clarity of illustration, however, the electro-magnetic vector H with its several components, as well as the inclined reference plane FL have been omitted from Fig. 2 and a vertical plane F-D has instead been passed through the line FG so as to contain the vector OV.

In addition, a second ray of the arriving electro-magnetic W ave has been represented by the vectors P202, O2N2 and O2V2 which represent respectively the direction of propagation and the horizontal and vertical components of the electro-static vector at a second reference point 02.

An H type Adcock array A is shown with its horizontal'lirnb lying in the reference plane B-C and its dipoles extending half above and half below this plane. If such array were responsive solely to vertical polarized energy, which would be the ideal case, a null reading would be obtained with the array rotated so as to lie in the plane FD. In practice, however, such an Adcock array is always slightly responsive to horizontal polarized radiation, and the array A may thus have to be rotated as shown so as to deviate by an angle 02 from the plane FD. Under some conditions the phase with which the horizontally polarized energy arrives at the receiver of the array may be exactly opposite to the phase with which the vertically polarized energy arrives at such receiver (in spite of the fact that the vertically polarized energy is differentially received so as to give a maximum of signal at the time of maximum rate of change of the vertical electric vector rather than at the time of the maximum value of this vector). If this phase relationship exists, a sharp apparently perfect null will be obtained when the array A is rotatedto a certain position inclined with respect to the plane F-D as shown.

The magnitude of the angle 01 (representing the deviation of the array from plane FD at the time that the false null is obtained) depends upon the relative sensitivity of the array with respect to the vertically and horizontally polarized wave energy, as well as. upon the ground angle 9 and polarization angle a of the wave. There are several factors which tend to make the angle (1 rather large even when the sensitivity of the ar-.

raywith respect to horizontally polarized energy magnitude of. the corresponding vertical com-i ponerit (D VT For the standard ave having a ground'angle of 45 and a polarization angle of 45 the horizontal component exceeds the vertical'component by more than 73%. Thus, for

10 fmicr'o-volts' per meter of vertical intensity there would be 17.3 micro-volts per meter of horizontal intensity in astandardwave. In the second place, the Adcock is designed to receive vertically polarized energy in a differential fashion; and thus, if the wavelength is long 'as compared to the separation between the two' dipoles, it may very Well happen that the maximum diiference between the voltages intercepted on the two dipoles may be less than the maximum voltage intercepted by either one. Thus, with dipoles one meter high and one meter .apart and a wavelength of say eight meters, if the vertical field strength he assumed to be ten micro-volts per meter, the maximum voltage intercepted by each dipole will be ten microvolts; The maximum difierence in the voltages intercepted by the two dipoles, however, even when the array is turned in the direction for maximum reception (1. e., perpendicular to the,

plane FD) would be only 7.7 micro-volts.

In the third place, sincethe Adcock is used in a 'null 'manner for determining directions, no useful signal resulting from the vertically polarized wave will be received when the Adcock is in truly correct position. Even when the Adcock is turned as much as from itstruly correct position (i. e. when angle 11 of Fi 2 is 5), the useful reception of vertically polarized energy is only 8.7% of the maximum possible reception (i. e. 8.7% of 7.7 micro-volts in the example above assumed).

Thus, if the three efiects are considered together, a standard wave of B-meters wavelength actingupon an Adcock which has two l-meter vertical dipoles joined by a l-meter horizontal transmission line could produce in the horizontal transmission line 25.8 times as much voltage as could be usefully produced as the difierence between two vertical voltages intercepted by the dipoles when the array is 5 from plane FD. This means that even if the shielding and degreeofbalance of the system is so great that only 4% of the energy intercepted byrthe horizontal transmission line is received in the associated receiving equipment, an error of more than 5 mayoccur if the phases of the horizontal energy transmitted to the receiver and the vertical energy transmitted thereto are such as to oppose one another. It is therefore clear that'anAdcock to give reasonably accurate indications should be designed to be insensitive to horizontal radiations to the highest possible degree.

j The manner in which such reduction in sensitivity to horizontally polarized radiation is attained in accordance with the present invention can best be seen from Figs. 3, 4, 5, 6 and '7.

' Fig. 3 represents the simplest form of Adcock array wherein the vertical dipoles [-2 and 3-4 are directly galvanically connected to the horizontal'transmission line 56 which is, in turn, connected over the vertical line 89 to the receiver and indicator I0. If the arms I and 4 .are -on meter apart horizontally; the differencedelivered to irifpctentiai'between these arms in u e resence' ofa'horizontal component of 17.3 micro-volts per meter would naturally be 17.3 'm'icro-volts. The; presence of the shield; however, somewhatreduces themagnitude of the potential difference sincethis shield is an excellent conductor-disposedhorizontally in the immediate vicin-i-ty-of thedip'ol'es' and thus acts toattenuate the-horizontal electric component in its immediate' vicinity. "--If;-t'he shield ll could be consideredto'be at all times an equi-potential surface, the attenuation of v the horizontal electric component----immediately adjacent this shield would-=becompleteE In practice shield ll, al-- though it-may-have negligibleresistance, ordinarily has a very substantial inductance and thus is far from being-an equi-potential surface.

In accordance with one feature of my inven-- tion shield H is rendered of farlower impedance,

and therefore more nearly an equi-potential stir-- face, by providing between its ends additional conductor means R, asshown in Fig. 4, which is a plan of a simple Adcock such as shown in Fig. 3 with added conductors according to my invention"; These conductor means R, together with'the'shield ll itself, form a flat network orwebofconduct'ors which therefore has a -comparatively low inductive impedance and thusmore'nearly approaches an equi-potential sur-" face; Bythis means the strength of the horizontaL electric component in the vicinity ofthe Adcock array is diminished, thus-greatly diminishing the flow of parallel currents over 'the two wires '5 and 6 of the horizontal transmission line.- In accordance with a'further feature of my invention illustrated in Fig. 5, conductor means S are also extended outward from the shield II in a, horizont'aldirection so as to extend well outside of the dipoles, and preferably also additional conductivemeans such'as Rm. are extended to-meet these extensions S so as to reduce the inductance of the latter. By these arrangements the horizontal electric component between the dipoles and in the vicinity thereof is very greatly attenuated. such attenuation of the horizontal electric component may-be considered as 'result ingfrom 'a refi'ection (with reversal of electro static'phase) of-"the horizontally polarized component arriving at'the network II, R, Ra, S. Such reflection decreasesthe horizontal electric com-- ponent to zero in the immediate vicinity of the flat conducting network which produces the reflection.

It may be noted that the conducting arrangementsapplied, as shown in Figs. 4 and 5, are es senti'ally .confinedto a horizontal plane and therefore produce substantially no efiect upon the vertically polarized energy arriving in the vicinity of the Adcock array. At the same time these arrangements very substantially reduce the;

formers or other coupling arrangements. preferred-type of coupling arrangement for such an Adcock is illustrated in Fig. 10, the coupling being here effected not only through transformers I5, I6 but also through two pairs of coupling triodes I'II8 and I92II, which are connected with their load resistors on the cathode sidesoas to produce a large amount of negative feedback. Preferably, these tubes have ahigh inherent volta e amplification factor but because of the negative feedback the effective voltage gain thereof is smaller than unity (e. g. about A to .7 for a mutual conductance of 5000 to 9000 micromhos) and is very nearly independent of variation in supply voltages, tube characteristics, etc.

The schematic representation of Fig. 6 which shows the dipoles I -.2 and 3-4 coupled to the line 5,6 should be understood to represent either a transformer coupling or a transformer and vacuum tube coupling such as shown in Fig. 10, or any other type of isolating coupling, although a plain transformer coupling is illustrated to simplify the drawing of this figure.

Comparing Fig. 6 with Fig. 3 it will be noted that the parallel currents in wires 5, 6 resulting from the horizontal electric component will be eliminated, except to the extent that distributed capacity through the transformer or other coupling means permits a current fiow from dipole I2 to the wires 5, 6 and thence out to the dipole 34. In spite of the substantial suppression of the parallel currents due to horizontally polarized electric energy however, some reception of such horizontally polarized energy may still occur if the halves of one of the dipoles, such as I2,,are unbalanced. Let us assume, for example, that the limbI is somewhat longer than the limb 2. At first sight it might appear that in spite of such unbalance no horizontally polarized energy could influence either of these limbs. If consideration is given to the presence of shield II which constitutes essentially a horizontal conductor, it will be noted that such shield I I will'receive the horizontally polarized energy, and re-radiate this in a form havin some vertical components so as to enable this energy to influence bothof the. limbs I and 2. From another viewpoint the transfer of energy from the horizontal electric component of the arriving wave to the limbs I and 2 of the dipole may be analyzed as follows.

The arriving horizontal electric energy excites shield I I so that the latter develops standing voltage waves along its length, the voltage being maximum positive at the left end of shield II at the instant when it is maximum negative at the right end and zero in the center. The electroa static coupling between shield II and limb I is such that the inherent capacity of the upper end of limb I is fairly equally distributed over the left and center portions of shield II while the electro-staticcapacity of the lower'part .of'limb I extends in .much larger proportion to the .ex.-. treme left end of shield II than to the more re-' only net effect would be a small currentfiowing simultaneously in both limbs I and 2 and out through the distributed capacity of the-coupling transformerto the shield II. If the coupling transformer itself were also perfectly balanced,

The-

such current would have no effect upon transmission line 5, 6 or upon the receiver I0.

- In practice it is very likely to occur either that the dipoles I or 2 are unequal with respect to electro-static capacity with regard to shield II thus giving a current flow from one limb to the other or that the coupling transformer will be slightly asymmetric so that the previously mentioned flow of current from the limbs in parallel through the transformers distributed capacity to the shield II will set up a slight current in the secondary of this transformer. As previously mentioned, in connection with the analysis of Figs. 1 and 2, even a 4% unbalance would lead to an error of more than 5.

Furthermore, it should be noted that even if the distributed capacities of the coupling transformer could be. perfectly balanced and the sizes and shapes of the two limbs I and 2 made identical, some asymmetry is likely to occur by reason of proximity to the ground or other objects, or even by reason of the proximity of the shielded down lead 8, 9. It will thus be clear thateven with the improved type of Adcock shown in Fig. 6 wherein the dipoles are isolated from the horizontal transmission line 5, 6, it is a difficult matter to attain by balancing alone a satisfactory degree of freedom from response to horizontally polarized energy. In accordance with the present invention a very great improvement in this respect can be effected by providing additional conductive members R as shown in Fig. 4.

As previously described the effect of such additional members is to form with the horizontal shield I I a fiat conducting network whose overall inductance is exceedingly low. The whole network thus formed tends more nearly to approach the characteristics of an equi-potential surface, and the voltage differences between the different portions of the shield II are very greatly reduced. By such reduction of these voltage differences the pickup of energy by the limbs I and 2 is very nearly eliminated. If the pickup is considered from the standpoint of re-radiation it will be clear, that the resultant of the arriving wave and the re-radiated wave will be almost zero in the vicinity of an equi-potential surface and therefore the pickup by dipoles I and 2 willbe substantially negligible. If, on the other hand, the pickup of energy by these limbs is analyzed as being produced by the diverse coupling of different portions of the limbs to different portions of shield II through the distributed capacities thereof, it will still be seen that a reduction in the voltage differences between the different parts of shield I I will largely eliminate such pickup.

The arrangement ofv Fig. 5 wherein the members S are extended beyond the'dipoles I and 3 will also be found advantageous with the isolated type of dipole illustrated in Fig. 6, although at first sight the advantage of such an arrangement may not be apparent.

Fig. '7 will be helpful in illustrating how the addition of extensions S still further reduce pickup of horizontally polarized energy by the limbs I and 2. In Fig. 7 shield II and the extensions S are shown as being of equal length, and the limbsI and 2 of the dipole are shown as being of exceedingly unequal length. Such an exaggerated showing is merely'made to render the theory more clear. Referring to Fig. 7 it should be noted that, even if the limb 2 were completely removed, no energy could be induced in the limb I in response to the pickup of horizontal electric 9 energy by the shield ll and extensions S, if the latter are perfectly symmetrical about'the limb l;""the reason for this is that the right end of shield H would become negative at the same time that the left end of extension S became positive, and the effects thereof upon the limb would mutually cancel. I 'On the other hand, as previously pointed out and as schematically illustrated in Fig. 8, the pickup by the limbs l and 2 would be equal and would thus tend to cancel if these two limbs were identical (and coupled through a perfectly balanced coupling transformer), even though the extension S was made negligibly small in comparison to the shield I I. By providing an ex tension S which extends out beyond the vertical dipolea substantial distance (desirably at least one-third the length of one of the dipole limbs and preferably twice' this much) the amount of voltage picked up by each limb of the dipole due to horizontally polarized energy is reduced very substantially. At the same time, the balancing effect due to the two dipoles is maintained. Thus, both the balancing effects of Fig. 7 and Fig. 8 are present to some degree and thereby the amount of pickupof horizontally polarized energy is reduced to a negligibly small value. e

f'Ifhe foregoing descriptions have been based upon the assumption that the Adcock array, whether of the simple type shown in Fig.3 'or of the isolated-dipole type shown in Fig.6, con-- sisted of a single H rotatably mounted.- In other words, it has been assumed that theAdcook array comprised only two dipoles and one horizontally disposed interconnecting transmission line, the whole array being arranged to be rotated for determination of the nulled direction. While suchan arrangement may well be used for very shortwavelengths, it is preferable in very many casestoemploy a double Adcock array consisting oitwosuch H s mounted at right angles to each other and coupled toa goniometer so that by rotating the goniometer. the effect of rotating a single H'array may be attained without actually physicallymoving any part of the antenna array. f .In accordance with the preferred form of my invention such a crossed H Adcock array is em- 1o closed meshes rather than a 'solidbonducting sheet. The meshes of the network taken to gether should enclose a large area. A solid sheet which provided closed conducting'paths enclosing an equal area would be unnecessarily heavy and would offer an unnecessarily large wind resistance. I q 3 It is a further object of my invention to minimize also the omni-directional sensitivity with ployed,and. theihorizontal' conductive web is formed by joiningftogether the two shields .ll

and ll! of .the, two l-Ltype antenna structures, and by arranging additional conductors R so as tojnterconnect these crossed shields l l and I l",

asfshown in Fig. 9 In sucha form extensions S, may,conveniently be formed as the extensions of conductors R and of the shields II and l l',' respectively. If desired, the ends of these extensi'o'nslSl may beinterconnected with each other and with the links R by means of additional links R a SO as to minimize. the inductance of such extensions. Such'a n arrangement is shown in the upper andflowercorners of Fig. 9. Alternatively, the extensions S may. be open-ended as shown at the other two corners of Fig. 9., Preferably, all

four. corners .of one array aretreated in thesame fashign so thatjall four corners have the extension S open-fended, oralternatively all four cor-j hers are provided with cross links ,Ra.

-l g l s Qfth .netw ii t d y eitensiofis.

1 I1 and covering the area bounded by the four dipoles, is made in the form of a network of respectto vertically polarized energywhich occurs by reason of the so-called "high anten'na" effect. The nature of this effect can best be understood by reference to Fig. 11 which again represents a simple directly connected H type Adcock similar to that shown in Fig. 3. In' orderi to more clearly point out the nature of the fhigh antenna? effect this array is shown as having a; height T several times greater than the height t of its individual dipoles I2 and 3-4. Fur-5 thermore; for definiteness in discussion a portioir of the receiving and indicating equipment l0 ha s; been shown in detail, this portiongcomprising'a shielded input transformer 2|. j

As clearly shown in Fig. 11, the mean height T of the antenna array as a. whole is several times greater than the effective difference in'heightt ofthe two limbs of one dipole. Accordingly, the variations of potential of a complete. dipolej l with respectto ground are far greater thanfthe differences in potential of thetwo sides of such a dipole, thus resulting in large parallel currents whichfiow into all limbs of all dipoles co-phasally and then flow co-phasally down over .thetwo. wires 8 and 9 of the vertical transmissionline,

\ thence. by distributed capacity from the primary of transformer 2| tothe shield thereof and then, to ground. If the transformer 2|. .is'perfectly balanced, such currents will produce no effect in the secondary of this transformer but, as'previously mentioned, aperfect balance isnotfjread ily attainable in practice. In most actualdirection' finding systems therefore a very .substan-A tial amount of energy is receivedfrom thevertii cal electric component of an .arriving' .wave..jeyen when the antenna array is in such .position that a null should be received. It hasalready been proposed to minimize-this ,high antenna effect by isolating the dipoles of theAdcockarraywith transformers or otherisolating means asn ches. matically, shown in. Fig. 6. Since all trans; formers have some distributed capacity however; any unbalance in such isolated-transformera. 91. in the dipoles themselves, will prnduceflcirc'lllelling currents. .It is therefore ,desirous-to minigmize, as far as possible the amount. of fpickup, due to the high antenna effect. In order. to better understand how this .may beeflected in accordance with my invention it will be useful to consider the schematic diagrams of Figs. 12 and Q Fig. 12 schematically representsa. galvanically connected type H Adcock whoseshieldtl. has been modified so as to completely surround both dipoles of the array. Neglecting the'obvious fact that such an arrangementwould eliminate. the useful reception, it will be apparent that no parallel currents-will be produced in wires 8,.9 .as a result of the difference in potential. between grcund.and the limbs of any ofthe dipoles.v This freedom from parallel currents int, .9. .will still beobserved even though the inductanceof shield H prevents it from all being continuously at ground potential, provided only that -the re-, sistance ofthis shield Ill isnegl-igible, whichis usually the case.

As. a result of. the inductance of the shield. it would actuallybefound; in the case of. the apparatu's of: Fig. 12,. that the potential at. different points 21 through 38 of the shield ll would vary in the manner indicated by the curve in. Fig. 13. Nevertheless, if the conductivity of the shield were adequate practically no current wouldv flow in any of the wires enclosed by such shield.. The explanation'ot this is-somewhat asfollows: When the end portion of the shield H risesto thehigh potentialirepresented in Fig. 13 as betweenpoints 2] and 38, the whole dipole l2 which is. enclosed within this portion of the shield, rises. to substantially the same. potential withoutthe. need for the addition ofany electrical charge tobring ittcr this potential; The reason forthis is that the dipole l2.hassubstantially zero distributed capacity with respect to. earth since practically all. of its distributed capacity closes upon the sur face of the shield near points. 2I-3.8. Therefore,v when these parts of the shield have at. potential of. say, 10 millivolts, the potential of. the enclosed dipole l2 would. inherentlybe about-l millivolts even if this dipole were wholly insulated and. even if the wires 5, 6 were eliminated to prevent any. flow of current into or out, of the dipole.

In the arrangement of Fig. 11, however; the dipole l2 has. a very substantial distributed capacity to ground and, in addition, has a great deal of further distributed capacity which closes upon points of the shield ll, such as points 35, 34 remote from the. dipole. Therefore, in order. to bring this dipole |Z of Fig. 11 to a potential of say millivolts, a substantial current. is required even if the adjacent portion 36- of the shield II has! already been. brought to a. potential of 10 millivolts. This substantial current is necessary to chargeto 10.. millivolts potential. these portions oi the dipoles distributed capacity which close upon the grounder uponsuch points as 35, 34, 33, etc. No current is needed to charge those portions. of the distributed capacity which close upon portion 36 of. the shield, for this portion 36 of the shield is at. the desired potential of 10 millivolts.

.Although it is not desirable to enclose the dipoles in the manner shown in Fig. 12 since this would. eliminate all useful reception, an effect somewhat similar in nature can be obtained by the provision of a network of. the type shownin Fig. 5' or Fig. 9 which extends over a substantial horizontal area around each dipole. When such network is provided. it will be found that a very large portion of the natural capacity of'a dipole limb, such as limb I, will close upon the network thus formed. The result will be that there will be a substantially Smaller distributed capacity between the limb l and ground (or between the limb l. and some lower voltage part of the shield such as point 34 or 33). Even if the dipoles ar galvanically connected to the transmission lines as shown in Fig. 11, the magnitude of the high antenna effect will be substantially reduced and the parallel currents flowing in the transmission lines 8 and 9 will be considerably smaller than if the conductive network had not been provided.-

The amount of reduction of the high antenna effect which is obtainable by provision of a conductive low impedance network. in the horizontal planev is ordinarily not suificient and therefore I prefer that in addition to this measure some means be provided for isolating the dipoles |-2 and 3-4 from the horizontal transmission line 56. Such isolation may be effected by a plain coupling transformer or by a coupling transformer with grounded shielding between itswindings, or preferably by a combinationv of. acoupling transformer and triode coupling means as shown in Fig. 10. Even-when some such arrangements for. isolating the dipoles from the horizontal transmission line are provided, the provision of a horizontal. planar conductive network, such as illustrated in Figs. 5 and 9, will still. be found advantageous for reducing the high antenna effect, as well as for reducing the responsiveness to the horizontally polarized energy.

. It will be understood that any fiat conductive structure having closed conductive loops which surround a reasonably large area can be used. A solid sheet would give the required electrical effect although I prefer a network of closed meshes such as shown in Figs. 4, 5 and 9 because of its reduced weight and wind resistance. The'i-nvention is particularly advantageous when appliedto a crossed H -Adcock (having four dipoles andtwo horizontal lines). When so applied thetwo tubular shields of the two horizontal transmission lines. are preferably incorporated as part of the network asshown in'Fig. 9.

Alternatively, however, a network may be constructed as a unit and then applied to an Adcock. Such a network could be made up of five circles and four rods as shown in Fig. 14, being welded atall the intersectionv points such as 40, and at all tangent points such as 41:. The relative size and position of the Adcock for which the network is designed. is shown dotted in Fig. 14. Preferably the network should be electrically connected to the crossed horizontal shields of the Adcock at points 50, if not at all points where it crosses them. The network as. shown in Fig. 14 encloses an area somewhat smaller than the area of the square marked by the dipoles of the corresponding. Adcock. It would be better if. a rod were connected between the points M, other rods. being similarly connected between other corresponding points to. make the area enclosed by the network larger than the area. of the square. marked. by the dipoles. Very useful effects can be, observed with. networks which enclose only one-fifth the. area. of. said square.

Althoughl have describedmy invention .in particular in. connection with applications, wherein horizontally polarized components of the electrostatic vector E are undesirable, it is. clear that the principles thereof. are equally applicable where, say, vertical polarization is undesirable. In such cases, it is of course clear that the. above. discussion is. applicable when. considered in. a. quadrature sense, that is, with the dipoles disposed horizontally and the shielding structure normal thereto. I

Even though I have shown and described certain embodiments of my invention for purposes of. illustration it should beunderstood that. modifications, adaptations and alterations thereof occurring to one skilled in the art may be made without departing from. the scope of my invention as. defined in the appended claims.

What I claim is:

l. A directive antennav array including dipole antenna means oriented in a given longitudinal sense, and conductive shield means lying in a plane substantially normal to said dipole means having one part surrounding a. transmission line and a second part defining a two-dimensional structure extending laterally from. said first. part intermediate the ends thereof.

2.. A directive antenna array includng two dipoles interconnected by a transmission line and disposed parallel to each other, shield means shielding said line, and means connected to said shield means and forming therewith a two-dimensionally extensive conductive structure lying substantially in a plane normal to said dipoles and including closed conductive meshes of substantial area.

3. A directive antenna array comprising two generally vertical dipoles interconnected by a generally horizontal transmission line, shield means shielding said line, and means forming a two-dimensionally extensive conductive structure lying substantially in a plane normal to said dipoles and including closed conductive meshes of substantial area.

4. A directive antenna array comprising two generally vertical dipoles interconnected by a generally horizontal transmission line, shield means shielding said line, and means connected to said shield means and forming therewith a two-dimensionally extensive conductive structure lying substantially in a plane normal to said dipoles and including closed conductive meshes of substantial area.

5. An array according to claim 3, further comprising additional conductive means connected to said conductive structure and extending out beyond each of said dipoles.

6. An array according to claim 3, further comprising additional conductive means connected to said conductive structure and forming closed conductive meshes of substantial area.

'7. An array according to claim 3, further comprising isolating coupling means coupling said dipoles to said transmission line in respect of 14 transverse currents while providing substantial isolation thereof in respect of parallel currents.

8. A directive antenna array comprising four generally vertical dipoles interconnected by two generally horizontal transmission lines, shield means shielding said lines, and means interconnecting said shield means and forming therewith a two-dimensionally extensive conductive structure lying substantially in a plane normal to said dipoles and including closed conductive meshes of substantial area.

9. A crossed H type Adcock array comprising four generally vertical, spaced dipoles and two generally horizontal lines interconnecting said dipoles, elongated shields for said lines, and conductive links interconnecting the successively adjacent ends of said shields.

10. A directive antenna array including dipole antenna means oriented in a given longitudinal sense, and shield means lying in a plane substantially normal to said dipole means and comprising a two-dimensionally extensive conductive structure wherein said structure includes closed conductive meshes of substantial area.

HENRI G. BUSIGNIES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

